VoLTE Must Prove Its Worth

We've been hearing about LTE (Long-Term Evolution) cellular technology for years, and the latest handsets now use it for data. The next step will put digitized voice over LTE. A full migration to VoLTE (voice over LTE) will take years because of legacy equipment, but it is happening.

In "Voice over LTE rollouts require new ways of thinking about test," Kethees Ketheesan wrote that VoLTE should deliver on the "promise of LTE by providing a service that replicates all the features of traditional voice and offers the end-user a superior alternative to OTT VoIP applications, which are now readily available over wireless networks."

For VoLTE to truly deliver on that promise, engineers must prove that it's at least as good as, and preferably better than, other voice technologies. That's the challenge facing wireless carriers as they roll out VoLTE. Third-party test labs such as Intertek offer VoLTE testing services to carriers, handset manufacturers, and chipset manufacturers.

"When voice moves to LTE," said Intertek's Gwen McNew in a phone interview. "It must be at least as good as, or better than, legacy technology from a consumer perspective. Those technologies have had a long time to stabilize voice, and they are very good. Carriers won’t deploy VoLTE unless they’re confident in the quality of service."

An 8100 LTE test system fromSpirent Communications.

Spirent Communications announced that Intertek now uses the Model 8100 LTE test system (see photo) to test handsets that communicate over the Verizon wireless network. Intertek uses the system to test equipment from other cellular carriers as well. What's new is the Verizon VoLTE testing, as Intertek has added VoLTe to its suite of LTE tests. Testing capabilities also include IMS (IP Multimedia Subsystem), VoIP, and E991. The handsets that incorporate VoLTE are in validation status, according to McNew. "We're testing beta versions of products with these technologies. These are not market-ready devices."

McNew explained that some test plans for the latest cellular technologies are now performed by third parties. Carriers are testing voice quality and voice reliability (call drop) with help from third-party test labs on other test cases.

Also on the call was Anil Khitolia of Spirent Communications, who explained how Intertek uses the 8100 LTE test systems. The diagram below shows how the system's components interact.

"The 8100 emulates LTE, 3G, and 2G networks," he said. "It connects to a cellular device through a coax cable to the device's antenna connection." Khitolia explained that the system performs IMS VoIP and VoLTE testing, analyzes audio quality, and performs stress testing on the device.

A typical VoLTE test case consists of connecting and powering the device and registering on the network. To complete the test, either the DUT or the tester initiates a call. During that time, the tester logs information passed between it and the device, which includes IMS messaging. The test system verifies that all messages passed between it and the DUT meet industry or carrier standards. Finally, the call is dropped.

A typical test can run for four to six hours. At the end of the test, the system reports on each test case run during a test session. Reports include number of passed and failed test cases. Engineers also get data that explains why a test failed.

If SIP is used to do call establishment, most of the challenges will be handled through IP layer. Potentially, the network architecture can get around from using Mobile IP. Yet, I believe with full support of mobile IP in the voice network and in the LTE network will be ideal.

Absolutely, to get unique IP end to end, IPv6 is necessary. Even so, there might be transition from one IP network to anther which will require Mobile IP and, potentially, SIP infrastructure to deal with. For IPv4, IP end-to-end can be achieved through NAT and private IP addresses. My smartphone is currently getting private IPv4 address. NAT will certainly happen somewhere.